It is convenient to carry and use a mobile handheld terminal such as a smartphone or a tablet computer. In addition, as the mobile handheld terminal develops towards multi-functionalization and high efficiency, a user may perform an activity at any time, such as video watching, online reading, online game, or instant messaging. The mobile handheld terminal is increasingly popular to the user. Compared with usage convenience of the mobile handheld terminal, a battery standby time of the mobile handheld terminal cannot meet the user's requirement. Therefore, an electronic product with an external charging function appears, such as a mobile power pack. To ensure device safety, these electronic products perform appropriate current-limiting setting on a charging current during external charging.
FIG. 1 is a schematic structural diagram of a current-limiting solution. As shown in FIG. 1, a specific principle of implementing a current-limiting function by disposing a dedicated linear current-limiting chip 12 in a post amplifier of a power supply chip 11 includes when the charging current is greater than a set current threshold, conductive impedance of the linear current-limiting chip 12 is linearly increased to reduce the charging current, until the charging current is equal to the set current threshold. Therefore, a limitation on the charging current is implemented.
However, the current-limiting solution has the following disadvantages. Because heat protection started by an external charging device is easily caused in an over-current state due to heat generated when the conductive impedance is increased, that is, a path loss is increased, the external charging function is disabled, resources are wasted, and charging efficiency is reduced.